Speed-reduction mechanism



Nov. 26, 1929. R. w. A. BREWER SPEED REDUCTION MECHANISM Filed A'pril2o', 1927 ss, W

Patented Nov. 26, 1929 UNITED STATES ROBERT' W. A'. BREWER, oFJENKINTOWN, PnN'NsvLVANIA, AssieNoR To HAROLD F. PITCAIRN, or BRYNATH'YN, PENNSYLVANIA SPEED-REDUCTION MnoHANisM Appliation filed April20,

This invention relates to speed reduction mechanisms and is applicableto numerous devices' an'd apparatus where itis desired to operate a*ldriven member at a lower speed than the member driving it. For purposesof illustration, however, I disclose the invention hereinasparticularly7 applied to a cam mechanism such ais used in a radialinternal combustion engine'.

Ambn'g the" primary objects of the invention are: to obtain speedreduction, even to high' ratios, with' the" least complication ofmechanisme;r to' obtain1 such reduction with apparatus of little weightand occupying a minimum ani'nu'ntof space, these considera tions beingof especial* importance in connection with airplane engines, in whichthe 1nveritinmay' be advantageously employed; to provide sn'c'lifamechanism in which there arev no dead' points in the direction ofpressure applied tothe driven member; and to provide multiple toothengagement between thedriven member andy the driving means wherebydistribution of pressure, quie'tness of operation, ediiction of lostmotion or ba'clil'ash, andlonger life of parts, are obtained. p

further object of the invention isto eliminate'l cumbersome trains ofgears with their attendant lost motion andI other disadvanta'gesinlspeed reduction mechanism.

StillV another object of the' invention 1s to provide a speedIred'iictinn`mechanis`m wherein th'e'drive'n member issubjectedlto"substan tially no tliriistlslorV forces except the torque imparted toit, Y

More specifically, I aim by my invention to provide' al speed reductionmechanism wherein the driven member'isipo'sitioned concentricallywiththe driving member and is driven'V by means of a crankl or eccentricoperating a strap which actuates preferably a plurali-ty ofl spacedgearseach-acting on said driven member and between which the load isfdistributed.y l

Still anotherobject of the invention is to provide" suchi ai mechanismwhich shall be simple-'n construction and readily assembled anddisassembled, and the partst et which,

1927'. Serial No. 185,123.

as they are assembled, will secure prior parts in place, serially.

How these objects and their attendant advantages', and others which areincident to the invention or which will occur to those skilled intheart, are obtained will beclear from the following descriptiontakentogether with the accompanying drawings, in which Fig. 1 is an endelevational view, with parts in section, of an engine constructionembodying my invention;

Fig. 2 is a section taken .on the line 2 2 of Fig. 1;

Fig. 3 illustrates a modified form of a portin of the mechanism; and

Fig. 4' shows amodiiication of another portion thereof. Y

Referring now to Figs. 1 and 2, it will be seenthat l have thereinillustrated aportion of a radial airplane engine having a casing 2 and acrankshaft 3 supported at a bearing 4l in the web'or other rigidstructure 5. Concentric with the shaft is a cam ring 6 having cams 7 bywhich the valve rods 8 are operated through their rollers 9 (only one ofwhich rodsiis shown, it being understood that there are a number of themspaced around the casingfr 2, one for each valve of the engine).

To drive the cam ring 6, at a properly reduced speed, from the shaft 3,I have interposed a' mechanism embodying the features andv advantages ofthe present invention, which will now be described.

On the shaft 3 is mounted an eccentric sheave comprising a lixedportion10, secured to the shaft, as by a key 12, and an adjustable' portion 11mountedA on the shaft and Secured to the fixed portion by a pin or bolt13' threaded into the fixed portion and eX tending through a curved slot14 in said adjustableportion. The sheave carries a bearing`15, which,when the i'ixed and adjustable portions 10 and 11 are tightly secured bythe pin 13,:is held between the flanges 16 and 17 on' the' fixed andadjustable sheave portions, respectively.

On the outer ring of bearing 15 is carried the eccentric plate or strap'18 which basan inner flauwe 1'9 toprevent its'slpping olf the bearing?ft'lafplurality of equispacedpoints on the strap, equi-distant from thecenter thereof, are holes, receiving pins 2O of cranks 20", in thisinstance three being shown, each of which is connected to, and adaptedto actuate, a toothed gear wheel or pinion 21 on a pin or shaft 22mounted in any suitable fixed structure, which in this instance is shownas an annular member or mounting ring 23 secured, as by bolts 24, to theweb structure 5. The throw of the crank 2Ob is, of course, the same asthe offset of the eccentric from the center line of shaft 3.

Positioned to be driven by the wheels 21 is an internal ring gear ormember 25 having teeth 26 engaging the teeth of said gear wheels 2l.`The cam ring 6, which Vvis positioned on the periphery of the fixedring'23 behind the flange 27 thereof, is 'secured to the ring gear, asby means of ears 28 on the latter and bolts 29. v

When assembling, the parts are put in in their order, it being apparentthat each will fit only one way and in one place, and the parts as theyare serially put in place secure prior lparts in position, the mountingring 23 retaining the cam ring 6 and the gear 25 secured thereto, andthe gears 21 with their cranks 20 being retained against the outside ofthe mounting ring, on their pins 22 by the strap 18, which in turn isretained by the bearing 15 secured by the eccentric sheave 10, 11, whichis fixed against rotation by the key 12 and positively retained endwiseof the shaft by the retaining nut 3b. The adjusting slot 14 in theadjustable portion 11 of the sheave is of sufiicient length that theeccentric lstrap may be shifted far enough to permit the correctrelative positions of the meshing gear teeth and the -cam lobes to bemade, and thus to permit of the proper initial adjustment of therelative position of the lobes to the main crankpin of the engine so asto time the operation of the various parts in their correct phaseposition. After such adjustment is made, and the adjustment pin 13 istightened, fixed pins 13al may also be employed, if desired, to insurethe permanency of the adjustment ofV the portions 10 and 11 of thesheave.

It will now be seen that in operation, since the center of shaft 3 andthe centers of gear wheels 21 are at fixed points, the rotation of theshaft carrying the eccentric sheave with it will cause a rotativeshifting movenient of the eccentric strap relative to each of saidcenters, thus rotating the gears 21 through one revolution for eachrevolution of the driving shaft, and the ratio between the number ofteeth on the gears 21 and the number of teeth on the driven gear member25 wiil determine the speed reduction. The ratio in the instant case isapproximately 10 to 1, but it is obvious that by a mere alteration inthe diameter of the pinions 21 employed (mounting them nearer to orfarther from the center, in proportion to such alteration) practicallyany desired speed reduction may be obtained, it being remembered thatthe crank throw of the gears must always be maintained the same as theoffset of the eccentric employed. In this connection I wish to point outthat I may provide for the ready use of gears of different diameters inany suitable Way, as, for instance, by providing inthe fixed ring 23 aplurality of sets of holes for mounting the gear pins 22 at varyingdistances fromv the periphery, and by providing a correspondingplurality of sets of holes in the strap 18 at varying distances from itscenter to receive the crank pins 20.

It is very important that there should be no lost motion or backlashwhen a mechanism of this character is employed to operate or controlrelative speed mechanisms which must at all times maintain correct andexact phase relation. In the.l construction herein indicated, at least 6teeth are always in engagement thus ensuring closeness of fit betweenthe tooth faces and a reduction of specific tooth pressure, which inturn militates against rapid wear of the parts in intermittent contact.A consequent feature of multiple tooth contact is, of course, quietnessof operation. i

It should the character described has no dead point in the lines ofpressure action and reaction because the circular pathof each actuatingpin 20, for example, is -in alll positions normal4 to the pressure faceof a pair; ofvteeth, when in engagement. 'i

In Fig. 3 I have illustrated a modification, in which, instead of aneccentric sheave, I provide on the end of shaftfa an eccentricallylocated pin 30 to actuate the strap 18a.

Fig. 4 illustrates a modification which may be employed when theinvention is used in an apparatus requiring greater power transmissionthan required in connectionv with the device of Figs. l and2. In thisinstance I have shown the pin vor axis 22a, of the gear 21a(corresponding to the gear 21y of the first two figures), 'prcyidedrwith an additional support or bearing 31 in front of the gear, inaddition to its bearing in the fixed ringv 23a in back, so that thecrank 20a will be immediately adjacent a bearing support.

It will be observed that the invention as illustrated employs"v 'threesmall gears 21 meshing with the common'annular gear 25, (between wthichsmall gears the strap 18 may be considered as a linkagemeans) and whilethese provide la'well-ba-lanced support for the gear 25 and distributethe torque around its periphery, yet I do not limit myself to the use ofthree such gears, for a di'ere'nt number might well .be used, and otherchanges in the details of construction bemade, without departing fromthe Vspirit and scope of my invention.

be noted that a mechanism of I claim 1. A speed reduction mechanismcomprising, in combination, an eccentric sheave actuated by a drivingmeans, and adjustably related thereto, a strap operated by saideccentric, a plurality of pins actuated by said strap, said pins formingcranks having a throw equal to the throw of the eccentric, a pluralityof gears rotated by said cranks,

1g and a common gear member associated with and acted upon by saidplurality of gears.

2. In an internal toothed gear speed reduction mechanism, a mountingring forming a bearing retaining the internal toothed gear in position,journal pins associated with said mounting ring, driving pinions andattached cranks slidably located on said journal pins, a shaftconcentric with the internal toothed gear wheel, and a common actuatingcrank mechanism mounted on said shaft having positive endvvise locationretaining the driving pinions in position on their journal pins.

In combination a driven member, actuating mechanism therefor includinglinkage means, a driving shat't concentric with said driven member, anddriving means having one portion iixed to said shaft and another portionadjustably associated with the tixed portion and transmitting motionfrom the shaft to said linkage means.

4,. A speed reduction mechanism comprising, in combination, an eccentricsheave actuated by a driving means, and adjustably related thereto, astrap operated by said eccentric, a plurality of pins attached to saidstrap, an equal number of gear Wheels with each ot which a pin co-acts,and a common gear member associated with and acted upon by said gearWheels.

In testinmony whereof, I have hereunto signed my name.

ROBERT W. A. BREWER.

